This invention relates to burners which utilize a pressurized supply of fuel and which vaporize the fuel prior to combustion.
Liquid-fueled burners that do not require any external source of power are in common use as portable heat sources for applications such as campstoves and military field kitchens. Generally such burners store the fuel in a pressurized fuel tank and vaporize the liquid fuel prior to combustion in order to provide for complete mixing with combustion air and in order to provide a pressurized gas stream to propel the mixture to the burner head. In the past, most such burners utilized highly volatile fuels such as gasoline or kerosine, since these fuels vaporize at a low temperature, making it easy to heat the vaporizer and maintain the fuel in the vapor state. Operation with less volatile fuels, such as diesel fuel, is far more difficult, since diesel fuel vaporizes at a relatively high temperature, on the order of 600-700 degrees Fahrenheit, making it far more difficult to heat the vaporizer and to deliver the fuel to the burner as a vapor. Moreover, at elevated temperatures liquid fuels tend to decompose, resulting in the formation of carbon and tars which foul the vapor passages. Nonetheless, it is highly desirable to use diesel fuel, since it is much safer than gasoline and is readily available in the military, which uses it as a universal automotive fuel.
Prior-art burners exist that are capable of burning liquid fuels without an external source of power. The vaporized fuel is generally accelerated under pressure in a nozzle, and the resulting fuel vapor jet entrains some or all of the air required for combustion. A common example of this class of burners is the "Coleman Stove", which utilizes a closed fuel tank which is pressurized by pumping air into the fuel tank. The fuel is forced out of the tank by action of the tank pressure and flows through a "generator" in which the fuel is vaporized. The heat necessary for vaporization is provided by a "pre-heat burner" during start-up, and following the pre-heat period, by heat from the main burner. The generator may take many forms, but commonly takes the form of a tube heated on the outside by a preheat burner, and once the main burner is ignited, by the main burner flame. From the generator, the now-vaporized fuel flows through a nozzle in which it accelerates to a high velocity, and then mixes with and entrains air for combustion. The air/fuel mixture then flows to a burner head, which anchors the flame. A fuel valve is generally provided to modulate and/or shut-off the flow of fuel. The fuel valve may control either the liquid fuel or the vaporized fuel.
Other examples of prior-art, non-powered, vaporizing, liquid-fueled burners include:
MSR X/GK campstove (gasoline, kerosine or diesel fuel) PA0 Optimus 199 Ranger (alcohol, gasoline, kerosine) PA0 Coleman Peak 1 (gasoline or kerosine) PA0 Optimus III Hiker (gasoline or kerosine) PA0 U.S. Army M-2 Gasoline Burner Unit (gasoline) PA0 Haas+Sohn V75/1 Type Multicombustible Burner (gasoline, kerosine, diesel fuel) PA0 Karcher Field Kitchen Burner (Gasoline, kerosine, diesel fuel) PA0 Slow Start-Up--Many burners, particularly those of larger capacity, are slow-to-start because of the large mass of their vaporizers. PA0 Large Size and Weight--Some burners are heavy and bulky, which is a disadvantage in a burner intended for field use. PA0 Complex and Expensive--Some burners use complex and expensive mechanisms. PA0 Unsafe Operation--Some burners may allow unsafe operation by overheating the fuel tank or burner parts, allowing fuel to drip from the burner, or storing a large volume of vaporized, pressurized fuel. PA0 Unstable Operation--Some burners may operate in a pulsating mode or may be subject to flooding during start-up. PA0 High Maintenance--Most vaporizing burners are subject to fouling of the vapor passages by tars formed by the fuel. This problem is particularly acute in small vapor passages. PA0 Noisy, Dirty Combustion--Many burners produce smoky flames as a result of insufficient combustion air or poor mixing with air or require high air pressure to provide sufficient combustion air, which results in a noisy burner.
The first four prior-art citations are examples of small campstoves, typically under 10,000 BTU/hr output, that may be carried in a back-pack for individual use. The latter three citations are examples of field-kitchen burners having capacities on the order of 60,000 BTU/hr. It is somewhat easier to burn low-volatility fuels in the smaller burners since the entire burner and fuel delivery system may be heated by conduction from the burner head. On account of their larger size, it is more difficult to conduct sufficient heat throughout the larger burners to prevent fuel vapor from condensing in the passages leading from the vaporizer to the burner. The present invention is directed towards solving this problem in larger burners.
Prior-art burners suffer from a number of additional deficiencies which the present invention is intended to overcome. These include: